Wave guide feed for illuminating parabolic reflectors



y 29, 1952 L. c. VAN ATTA 2,605,419

WAVE GUIDE FEED FOR ILLUMINATING PARABOLIC REFLECTORS Filed Oct'. 11,1945 INVENTOR LESTER CLARE VAN ATTA MPW ATTORNEY Patented July 29, 1952WAVE GUIDE FEED FOR'ILLUMINATIN PARABOLIC REFI ECCITIQJRS Lester 0. VanAtta, Winchester, Mass, assign,

by mesne assignments, to the United Statesof ,7 America as representedby the Secretary of, the- Navy Application October 11, 1945, Serial No.621,834

My present invention relates in general to directive radio antennas, andin particular to means for illuminating a parabolic reflector withenergy from an open-ended wave guide positioned at the focal pointthereof.

In radio apparatus employing frequencies sufficiently high to permit theuse of wave guides for transmission lines, and parabolic reflectors aselements in the antenna systems thereof, it is convenient to construct adirective antenna of a parabolic reflector or paraboloid having anopen-ended wave guide transmission line mounted in and projectingthrough a hole at the center and along the axis of such reflector, up tobut not quite touching the focal point thereof. Energy emerging from theopen end of the wave guide may then be reflected to the paraboloid by asmall disc mounted on a suitable frame near the mouth of the wave guide.The reflecting disc and the mouth of the wave guide are usuallypositioned to include between them the aforementioned focal point.

A chief difilculty with this type of illuminating source for a parabolicreflector is that in effect a ring source of illumination is obtainedfrom the reflecting disc rather thana point source, and therefore, theenergy illuminating the paraboloid'cannot be made to come effectivelyfrom the focal point thereof. Consequently, the beam reflected from theparaboloid will be distorted and contain a relatively large number ofside lobes and the gain of the main lobe will be smaller than isdesirable.

It is therefore an object of my invention to provide illuminating meansfor a parabolic reflector that will produce a point source of radiationwhich may be adjusted substantially to coincide with the focal point ofthe parabolic reflector. Broadly, this object is realized by providingan'open-ended wave guide for illuminatingthe reflector, the open end ofthe Wave guide being located near the focal point of the reflector. Ametallic web lying in a plane perpendicular to the direction of the Evectors of the wave in the wave guide is mounted in the open end of thewave guide, and extends outwardly therefrom a short distance to includethe said focal point. An array of rod shaped antennasds mountedperpendicularly in this web and is arranged to provide a virtual pointsource of illumination. This point source is made to coincide with thefocal point of the reflector. As will be appreciated from the discussionhereinafter to follow, any conventional array of antennas may be mountedin the web of my invention.

19 Claims. (01. 250-33155) It is a further object of my invention toprovide such illuminating means that will be selfsupporting mechanicallyand require no external struts or framework. I

It is a still further object of my invention to provide suchilluminating means that will be able to be mounted in the open end of awave guide without interfering with or attenuating the energy passingtherethrough.

These and other objects and features of my present invention will becomeapparent upon a careful consideration of the following detaileddescription when taken together with the accompanying drawing, thefigures of which illustrate typical embodiments of my invention In thedrawing: I

Fig. 1 is a side sectional view of an antenna in accordance with myinvention;

Fig. 2 is a cross section along the line 11-11 of Fi l;

Fig. 3 illustrates the antenna of Figs. 1 and 2 incorporated in a systemhaving a parabolic reflector, the reflector being partly broken away;

Fig. 4.- is a top view of another antenna in accordance with myinvention;

Fig. 5'is a cross section along the line V-V of Fig. 4;

Fig. 6 is a cross section along the line VI-VI of Fig. 4; and

Fig. 7 illustrates the antenna of FigsJl to 6 inclusive in combinationwith a truncated parabolic reflector.

In Figs. 1 and 2, a rectangular wave guide I0, having an open end I Iwith the outer surrounding edges I2 of the top and bottom walls beveledtoward said open end II, has a flat web I3 mounted in said open end andextending outwardly therefrom along the longitudinal axis AA of the waveguide Ill. The Web I3, may be mounted in the open end I I of the waveguide ID in any convenient manner, as for example, by slotting thenarrow walls of the said wave guide and inserting the web I3 in theslots and soldering it in place. The web I3 may extend a short distanceinto the wave guide III. The wave guide III is adapted to carry electricwaves in a mode having the electric vectors E directed transversely tothe axis A--A, and the web I3 lies in a plane which is substantiallyperpendicular to the direction of said electric vectors E. First andsecond rod-shaped antenna elements I4 and I5 which each may be in theneighborhood of one-half wave length long are mounted substantiallyperpendicularly in and through the web I3 along an extension of the axisAA. The antenna elements I4 and I5 may have different I P located on theline between theircenters.

3 lengths, in the present example the one furthest removed from theopening ll being the longer. Thus the longer element may act in themaner of parasitic reflector with respect to the shorter element Hi, orthe shorter M as a parasitic director for the longer l5, depending: uponthe choice of length L1 and L2 thereof with respect to the length ofsaid electric Waves. Inthe present example, the two antenna elen ents l4and I 5 are arranged so that llOQQfihQlfllfl'fllfl appear to effect theinterchange of energy between the Wave guide It] and' 'space -at 'apoint Thus, when the system'of Figs; 1 and2 is radiating, the point Pseems to be a point source of 15 radiation. 1

The shorter antenna element Hi of length L1 is spaced outwardly from thopen end I l a distance (11 while the longer element 15 of length L2 is'spaced still 1 further nutwardly iromiith'e shorter e lement il adistaneeidzf'a ent from known antennaipractic'e" and lengths d1, d2, L1and Lzmay be variedmx t perimentaliy to providea desired paitter r't.fia'fspecific set of dimensions which l have foundfi sui't able forusein illuminating a parabolicfrefl'ectorf1 areasfollo'ws: 5 a r The lengthL1 of the' 'shorterelement 14 should be approximately 0.44Xji';Thea-length L2 of .the longer element 15 be approximately 0.501;. The.spacing di-may yaryiro'm 'the' lim'itdffCLlZf xto 0.16A; and.nfl Thespacing dz may var A to'0.20 V where A is the free spac'ei waveflengthiofithet 1 wave being. carried llfllh' lwave "guidell 0. Thesedimensions, however, are typical of a specific caseonly andnot th'onlydimensions tha t may 40 be used twitl1' this"antenna of myinventi'oir;In operation; energy. in the Wave guide l ii -havi-' in electric vectorsE may prdceed-rrcm rthe wave guide Ill into space through"fthaopen 'lend lii The antenna element [5 being of a length' -equal to a half wavelength will b resonant to these waves," and will startto radiatef Tha-shorter antenna element [4 acts as a parasiti' directorfor the longerantenna element i 5;--so thatthe two elements together radiate in -"'adirection which is back over the outer wall (jfffl'le wfi-Ve guideilliiacting '-at"the -sarne time as a point sourcecenteredatthejpointPQThis 19109 35845 reversedupon reception, inasmuchas an antenna will Work e'q'ually Well in both 'direetions the apparatusillustrated in Fig -l i h own mounted in and through an open 4? ing in aparabolic-reflector28} the wave guide -20 being co'axial with the aXisof the refiector-fiil and extending-toward but not reaching th-effoi'ialpoint P of that'reflector. Theeler'n'e'nts ld 'antt so'positioned 'thatthe point-P containedbet en; them is substantially coincident 'With th focal point'P of the reflector 29. CThus;- upon' trans mission, Crays "2Feman'atin 'g fror'n :th mouth -of theiwav'e" guide. illand'ithe-iarrayf-therein' will be reflected" irdmtthe refiector 2@tas acollimated beam of rays 22;I ILikewise,'in reverse, a'c'ollimatedbeamriofienergy oi" waves reaching the reflector Zil willrbe' broughtito*theafocal point B"; andiinto the:.wave guide i8. :Thus the antennaarray-of myrinventionmay-i be used for illuminating a parabolicreflector to "provide a narrow beam of energy having highgBLl'IILiIlithlIIlfiIjOl .ilobe ian'd; I simultaneously having lo iv: orsmalli minor "lobes;

Y betweemthe'llimits-6.13

- 'spectively.

" .33 and te'randthe web 32.

In Figs. 4 to inclusive, there is illustrated another embodiment of myinvention having a wave guide 3G with an open end 35 'anda Web '32therein similar to the web it of th embodiment of'Figsil and 9*. Thewefhzlils upports'two groups of rod shaped antenna elements; each groupcomprising first and second elements 33 and 35 re- Each group isarranged in a line which is parallel to the axis- B-B of the waveguideTSlT- Tli 'greups are spaced apart laterally substantially a halfWave length and preferably havetlie axis iB B'equidistantly containedbetwcen-'-t-hem.f Matching curtains are provided in"conventional-fashioni'or matching out the susceptance introduced by the array of antennasAgain, as in the apparatus of Figs. 1 and 2, the array comprising theantenna'elements 33 and 3 1 will aid in the interchange of energybetween the Wave guide 38 an'd free-space as if this energy-Were comingfi'om or entering the wave guide at a pointLP 1: contained amongthei'eleznents 3 3 and 3 4 'r'espec i tivel'y. Likewise, as in the'app'aratus of Figs I and 2, the Wave guide as is adapte'd to'cari y electric Waves-in Whiclr the"electri'c 'vector E is directed transversely tothe aXis l3- B ztnd thgweb 32 lies in a plane' substan y perpendieulalto vAClr the direction of 1 these electric "vectors E.

A specific -'set of "dimensions for the apparatus illustrated' in Figs-4 toG inclusive is as iollows': P The distance from each first radiator'33,".t'o the;

open end El -of thewave guide 391's 0 .l'72)\;,, The distance between afirst antenna element 33? and its associated. secondelementt lfis 0.25The lateral distance betweenigroups of antenna elements is /2 2 Asuitable distance between: the matchin curtain 35 and the opening "31 isH.446 These dimen sionsiwill provide an 'arrayl-in the openfend of theiWave guide 30 which is suitable-for-illuminating a parabolic reflectorast willxi'herein'aite r be explained. mHoweve'ryiit isnotice-understood that 1 these :distances'- and rdimensions #ar e'exemplary 1 only and not the only distances; whiclrgare suit iiablexior' use -with this antenna: of my iinventionf In. operation; theapparatus 'io'f rigs: etc 6f in elusive is similar'to; thev apparatus ofFigs; l and. 2, in that, energy proceeding from .the wave guide- 3ilwilllexcite'fthe antenna elements 3mm 34 into radiation since they areof substanti'ally resonant lengths. The first elements 33 rna'yact I asparasitic directors for a therespective second elements 34- ashereinabove set-- forth, thereby cau'sin'g'the' radiation to be directedback over the outer walls of the'wave'guide 38. Since there" are twogroups of antenna elements -33 and 34* side by side and spaced a" halfwave length apart in'acco'rdance with conventional antenna arraytheoriesrthe' beam will have narrowdire'ctivity in the plane of the web'32 with respect to the directivity in a plant perpendicular to thatweb? This is usuable in illuminating a truncated para' i I bolicrefle'ctor as will be now-explained-J In Fig. 7, the antenna of Figs.4-170 6 inclusive is mounted in and through a truncated parabolicrefiector' lfl having opposite portions X remove di' as by cutting alongsubstantially parallel chordsi The wave guide 38 is so positioned inthe'reflector- 40 that the E vectors-of the radiation-carriedtherebywill be directed horizontally! Again as"- Y before, the waveguide-3d is coaxial with the reflector 4fl' and'exte'ndsup tobut doesnot quit reach the focal 'P thereof; The array compris ing antennas 33and 34 is so positioned with re spect 'to' the parabolic reflector 40'that its point of radiation Pis'substantially coincident/with the focalpoint P: of the reflector 40. .I

Operation of the antenna of Fig. 7 is similar to the operation of theantenna of Fig. 3 except that the'beam will be somewhat fan shaped,being broader in the vertical direction than in the horizontal directiondue to the fact' that the parabolic reflector is truncated at the topand bottom and therefore does not have the resolving power or the beamforming power that it has in a horizontal plane. The provision of twogroups that all matter contained in the above descrip tion or shown inthe accompanying drawings shall be interpreted as illustrative andnot-in a limiting sense. It is further intended'that this invention isnot to be limited except insofaras is necessitated by the'prior art andthe spirit of the appended claims. i V

What is claimed is: l

l. A radio antenna comprising, an open ended wave guide adapted to carryelectric waves in a mode having its electric vectors directedtransversely'to the longitudinal axis thereof, a substantially flatmetallic web mounted in the open end of said wave guide and.projectin'g'outwardly therefrom in a plane substantially perpendicularto the direction of said electric vectors, and an array of rod-shapedantenna'elements substan tially resonant to said waves mounted atvarious points in said web substantially perpendicularly to the planethereof.

2. A radio antenna comprising, an open ended rectangular wave guideadapted to carry electric waves in a mode having its electric vectorsdirected transversely to the longitudinal axis thereof, a substantiallyflat metallic web mounted in the open end of said wave guide andprojecting outwardly therefrom in a plane substantially perpendicular tothe direction of said electric vectors, and an array of antenna elementscomprising first and second rod-shaped antenna elements substantiallyresonant to said waves mounted substantially perpendicularly in said webin spaced relation along a projection of said axis, one of said elementsbeing shorter than the other said array providing substantially a pointat which said waves are interchanged be},v

tween said wave guide and space.

3. 'Apparatus in accordance with clairna in;

which said first and second antenna elements" are respectivelysubstantially 0.4% and 0.5m long, said first element is spaced outwardlya distance equal to a value contained substantially between the limits012x to 0.167\ from the open end of said wave guide, and said secondelement is spaced farther outwardly a distance equal to tors, 'andanarray ofrantenna elements substana. I tiallyresonant to said wavescomprisingfirst and second laterally adjacent-linear groups of an?vtenna's', each group fcomprising first andsecond rod-shaped antennaelement's mounted substantially perpendicularly in said web in spacedrelationalong a line parallel to said axis, said-first elements being ofdifferent length than said second elements, said array'providingsubstantially a point'rat which saidi'waves are interchanged be-.

tween said wave guide and space. 0

5.. Apparatus in accordance with claim 4 in which said first elementsare each spaced outwardly; from said open end .a.;distance substantiallyequalto. 0172A, said second elements are each spaced further outwardlyfrom the associated first element a distance substantially equal to0.25- x, and saidgroups are spaced apart later-'- ally a:distancesubstantially equal to 0.50 A, with the: projection 'of saidaxis contained equidistantlybetween them, where x is the freespacelength 'ofsaidwaves.

6. A radio antenna comprising, an open ended Wave guide adapted tocarryelectric Waves in a. mode having its'electric vectors" directed trans-"versely to thelongitudinal axis thereof, a'parabolic reflector having afocal point, said wave guide being mounted in and through saidreflector' 'coaxiall therewith, the open end of'said wave guideextending toward "but not reaching mounted at various points in-said websubstantiall perpendicularly to'the plane thereof, saidarray providing apoint substantially coincident with said focal point at which said wavesare interchanged between said wave guide-and space.

7. Apparatus in accordance with claim 2 in which a parabolic reflectoris'mounted coaxially with the longitudinal axis of said wave guide andwith its focu substantially coinciding with said point.

8:. Apparatus in accordance with claim 4 in which a'parabolic reflectoris mounted coaxially with the longitudinal axis of said wave guide'and iwith its focus substantially coinciding' with said point." 9. A radioantenna a predetermined distance said wave guide.

10. A radio antenna comprising, an open ended wave guide, a dipoleresonant at the frequency of the high frequency Wave carried by saidwave guide, and means to support said dipole a predetermined distancefrom the open end of said wave guide.

11. A radio antenna comprising, an open ended wave guide, an arrayhaving first and second conductive rods substantially resonant t0 thehigh frequency wave carried by said wave guide, and means to supportsaid rods in a predeter mined spaced relation to the open end of saidWave guide to provide a desired radiation pattern,

12. A radio antenna comprising, an open ended wave guide, an arrayhaving a plurality of conductive rods substantially resonant to the highfrequency Wave carried by said wave guide, and means to support saidrods in a predetermined comprising; an open ended wave guide, aconductive rod resonant at the frequency of the high frequency Wavecarried by said wave guide, and means to'support said rod from the openend of spacedirelationshiprto thetopenend'tof said. wave guideto providea desired 'radiation pattern. I 13.1 A radio antenna comprising, anopen-ended);

carried by said wave guide,iand an array of :an'e. tenn'a 'elementscomprising first land second-rode shaped elements substantially resonant:to said wave mounted perpendicularly: in said'support in spacedrelation along a projection of the longitudinal axis'of said wave guide,oneof said ele-' ments'beingshorter than the'other, said arrayproviding: a spherical wave with its" origin substantially *a point.

14. Apparatus in accordance with claim 13 in 1 which-ta parabolicreflector is mounted :coaxially Withsaidlongitudinalv axisrof s'aidwaveguide" and Wit-h its-focus substantially coinciding with saidvpoint.

15. A wave guide feed fori-illumina'tinga rective high-frequencyantenna-of the'baraboli'c reflectortype; comprising '1 an' open" ended-Wave guide positioned coaxia'lly with' the axis of said I reflectorysaidwave guide extending toward but terminating before reaching the focalpoint "of said reflector, a substantially flat support rigidly mountedatthe 'open end of said wave guide in a planelpassing through saidi'focalpoint and perpendicular to the electric field of the 'ener gizingwavesbeing carried bysaid wave guide,

and an arrayiof parasitic antennas comprising. first 'andisecondisubstantially resonant rod shapedelements mountedisubstantiallyperpendicul'arly inzsaid support and disposed in a pat-: l tern toradiate toward said reflector a spherical wave whosetcenter oforigin'isatsaid'focal point. 16;TA .wave guideieed-forlilluminating'adi-t rective high frequency: antenna ofvthe'trum' catedp'arabola'reflector type comprising an'open 1 endediwave guide positionedcoaxially with the axisa ofsaidirefle'cton'said wave guide extendingtowardvbut terminating before reaching the focal point of saidreflector; a substantially flat support rigidly mounted at the open endof said wave gui'dei-inia plane passing through said 'focalpointrandiperpendicular:to the electric field of theienergizing'wavecarriedby said Wave guide} andian array of antenna elementssubstantially resonant to said wave comprising first and sec1-" 1y'perpendicularlyin said-support in spaced relation along. a lineparallel to said axis, said first elements being of different lengththan said secondielementspsaid array radiating a beam witha directionalpattermto ifeeda truncated'lx. parabola, said beam havingsa point of:radiation 1 coinciding with said-.focusapoint: I a

17; Radio transmitting antenna apparatus comprising a paraboloidalreflector defininga" di-r rective axis and a focal point, ultra vhigh:fre-- quency" energy", supplying; means extending? through saidreflectorsubstantially alongsaid axis to said-focal point for radiatingeinergyfirom the region of said focal,point-toward saidaren flector .toproduce energyjtransmission ina dl-jm rective pattern, and'c'onductivemeans supported b said energy supplying. means. and: positioned iintermediate said, focal point and said- :refle'ctor at a pointlseparatefrom saidaxisffor modify-,- ingv said directive transmission pattern-.1;

18. A directive radio antenna comprising-a paraboloidal reflectordefining adirective axis and-' afocal point, an/openended-wave guideextending through said reflector substantially jalong-c: saidaxis-toward said focal point; and a pluralityt; of resonantdipolesarrayed in l a predetermined spaced relationship to the open end ofsaidwave'e' guide fondirecting energy emerging frorn'saidzz I Wave guidetoward said refiector;-"

19. A directive radio antennaz'comprising a" paraboloidal reflectordefining a directive axis and a focal point, an openendedwvave-guide'extended through said reflector substantially alongsaid aXis toward said focal point, a supporting web mounted in the openend of saidwaveguidew and projecting outwardly therefrom -'in a plane*substantially perpendicular to the electric: field of I the wave carriedby'said Wave guide; and a plurality of dipoles substantially resonant-at--the:,- frequency of the wave carried' by said Wave:- guide, saiddipoles being arrayedin a predetermined spaced relationship in saidsupporting web for directing energy emerging from said, wave guidetoward said reflector.

LESTER C. VAN ATTA=- 3 REFERENCES, crrelo r The following references'areof recordrin the file of this patent: 1

UNITED STATES PATENTS 2,454,805 Kandoian Nov.- 30,

